Means for regulating the characteristics of multi-stage axial-flow compressors



y 0, 1956 A. c. LOVESEY 2,754,049

MEANS FOR REGULATIN HE CHARACTERISTICS OF MULTI-STAGE AXI -FLOWCOMPRESSORS Original Filed June 15, 1950 MEANS FOR REGULATING THECHARACTER- ISTICS F MULTI-STAGE AXIAL-FLOW COM- PRESSORS Alfred CyrilLovesey, Littleover, Rolls-Royce Limited, Derby, P y

Claims priority, application Great Britain June 16, 1949 4 Claims. (Cl.230114) England, assignor to England, a British com- This application isdivided out of copending application Serial No. 168,253, filed June 15,1950, now Patent No. 2,689,680.

This invention relates to multi-stage axial-flow compressors whichcomprise two relatively rotating bodies, hereinafter referred to as astator and a rotor. One only of said bodies may rotate or alternativelyboth may rotate in opposite directions. The invention has for its objectto provide a means of regulating the characteristics of the compressorin a desirable manner over a wide range of operating conditions.

The invention has special importance in relation to multi-stageaxial-flow compressors of the high compression ratio kind, such as are,for example, used in gas-turbine engines for aircraft, Where it isdesired to design the compressor to operate at high efiiciency,particularly in the upper portion of the speed range, corresponding tomedium or cruise power and maximum power conditions.

It is usual to design such a compressor to obtain efiicient operation ata particular speed, or at a particular value of a condition, such ascompression ratio, which is dependent upon speed, and such designinvolves the matching of the blade characteristics, including incidenceand profile, to maintain a desired flow condition within the compressor,at such particular speed or condition.

For example, the compressor may be designed so as to maintain a constantmean axial velocity of the working medium from the inlet to the outletof the compressor at a particular rotational speed of the compressorrotor, at a particular compression ratio, or at a particular correctedrotational speed of the compressor rotor. In order to give suchconditions, the shape of the compressor-duct, i. e. the annular passagefrom the inlet to the outlet of the compressor, and the incidence andshape of the blading are chosen appropriately, which results in thecompressor-duct converging as from inlet to outlet, the reduction incross-sectional area of the duct of the compressor compensating for theincreasing density of the working medium as it passes through thestages.

The annular duct will usually converge continuously from inlet to outletbut it may have a parallel sided portion, or even a slightly divergentportion, the actual design being such as to give a desired, usually aconstant, axial velocity of flow at each cross-section of the passage ata certain design condition.

As previously mentioned, it is usual to choose the cruise or maximumpower condition of running as the design condition for efficientoperation; at speeds below that corresponding to the design condition,when the pressure rise per stage is less than the designed pressurerise, there will tend to be an accelerating axial flow of the workingmedium from inlet to outlet of the compressorduct due to the overalldensity ratio being reduced compared with that at the particular designcondition. This acceleration appears as a reduction of the axialvelocity nited States Fatent of the working medium at inlet and anincrease of the axial velocity at outlet compared with those at theparticular design condition.

The blade incidence and shape, being appropriately matched to maintainefiicient operation of the compressor at the design speed, areincorrectly matched to maintain such operation at lower speeds, andfurther, particularly where the compressor is designed to operate at ahigh compression ratio, e. g. at 5 to 1, very serious difliculties areencountered in maintaining running at relatively slow speeds. Suchdifliculties, which are well known in the art, are attributable to thestalling of blades in the inlet stages of the compressor, due to thereduced axial velocity component of the working medium, which stallingmay result in a complete breakdown of flow conditions in thecompressor-duct.

Hitherto, it has been proposed that such difiiculties should be overcomeby the provision of means for adjusting the angular position of thestator-blades or of the rotor-blades, or of both, particularly in theinlet stages, for the purpose of varying the rotational swirl of theworking medium in these stages appropriately to avoid the stallingcharacteristic mentioned.

Another proposal has been that valve means should be provided forbleeding off a quantity of the working medium at a stage intermediatebetween the inlet and outlet of the compressor. This arrangementprovides for the maintenance of the axial velocity of the working mediumin the low pressure Stages of the compressor at a value approximatelyequal to that for the design condition with out increasing axialvelocity in the latter stages. The system, whilst providing certaindesirable characteristics, clearly results in undesirable losses, andfurther involves installation and control problems.

It will be appreciated that the problems outlined above are aggravatedwhen the compressor is designed for high compression ratios, as theconvergence of the compressorduct then becomes particularly marked; alsoin the use of high performance multi-stage axial-flow compressors inaircraft gas-turbine engines, the problem is further aggravated by thedesirability of obtaining efficient operation in a very wide range ofrotational speed and of altitude or intake pressure.

The main object of the present invention is to provide a novelconstruction of multi-stage axial-flow compressor in which the problemsoutlined above may be mitigated by adjusting, on change of rotor speed,the ratio, at the inlet of the compressor, of swirl velocity to axialvelocity of the working fluid to a greater extent adjacent the innerwall of the compressor-duct than the extent if any to which it isadjusted adjacent the outer wall of the compressor-duct.

The invention may be more readily understood from the followingdescription in which reference is made to the accompanying drawings, ofwhich:

Figure l is a sectional elevation of a compressor of the kind with whichthe present invention is concerned, and

Figure 2 shows a portion at the inlet of a compressor which embodies theinvention.

Referring to Figure 1, the reference numeral 10 indicates the rotor-drumof the compressor which is mounted for rotation about the axis XX and,together with the stator-casing 11, provides the walls of thecompressorduct 16. The compressor is a multi-stage compressor, eachstage comprising a row of rotor-blades 12, mounted on the rotor-drum 10for rotation therewith, and a row of stator-blades 13 mounted on thecasing 11. The compressor is also provided with a row of fixedguide-vanes 14 mounted in the inlet 17 of the compressor-duct 16upstream of the first row of rotor-blades 12.

The rotor-drum 10 is mounted on a shaft (not shown) which, at the inletend of the compressor is mounted in a bearing (not shown) carried bysupport webs 15 which extend acrossthe inlet 17 of the compressor-duct16 from the stator-casing I1.

The compressor is designed to give a compression ratio of to l at aselected rotational speed, and the compressor-duct 16. is dimensioned togive a constant axial velocity of the working fluid from the inlet 17 tothe outlet 18 at the selected rotational speed. As a result, thecross-sectional area of the compressor-duct 16 is greater at the inlet17 than it is at the outlet 18, i. e. the compressor-duct converges asfrom inlet to outlet.

Since the. incidence and shape of the rotor-blades 12 and stator-blades13 are appropriately matchedto give efficient operation at the selectedrotational speed, they are inappropriately matched foroperation at otherspeeds; and serious ditiiculties are encountered in maintaining steadyoperation of the which are low compared with the selected speed. Suchdifiiculties, which are well known in the art, are attributable, atleast in part, to the reduced axial velocity of the working fluidthrough the inlet stages of the compressor, which is liable to result installing of the compressorblades in these stages, which in turn mayresult in a complete breakdown of flow conditions in the compressorduct.

In constructions of multi-stage according to the present invention,backs are mitigated by increasing, when stalling is likely to occur, theratio of swirl velocity to axial velocity of the working fiuid passingthrough an inlet row of statorblades (i. e. a row of stator-bladesupstream of a row of rotor-blades which is liable otherwise to stallwhen the rotational speed is low) to a greater extent adjacent the innerwall of the compressor-duct than the extent of the increase, if any, insuch ratio adjacent the outer wall of the compressor-duct.

By doing this, two results arev achieved. Firstly the.

axial velocity of the work'ng fluid adjacent the outer duct wallisincreased, as compared with a similar construction in which theinvention is not employed operating at the same speed, so that theflow-conditions'adjacent the outer duct wall approach the designconditions more closely and the likelihood of stalling adjacent theouter duct wall is reduced. Secondly the direction of motion of theworking fluid relative to the succeeding row of rotor blades is adjustedadjacent the inner duct wall to provide adequate compensation for thereduction in axial velocity of the working fluid, and so reduce thelikelihood of stalling adjacent the inner duct wall as well. 1

One embodiment of the invention'is shown in Figure 2. In this embodimentthe inlet guide-vanes 14 are torsionally deformable. Each guide-vane 14-is anchored at its radially outer end to the compressoncasing 11 and, atits radially inner end, is provided with a trunnion 34 lying on an axissubstantially radial to the axis of rotation XX of the compressor rotor.

mechanism, including a crank 40 foreach guide-vane which engages witha-ring 41 common to all the guidevanes, is provided so that thetrunnions 34 of all the guidevanes can be rotated simultaneously so asto deform by torsion all the guide-vanes i4. When the trunnions 34 arerotated the ends of the guide-vanes adiacent the inner wall of, thecompressor passage rotate with them but the other ends of theguide-vanes are anchored to the casing compressor at rotationalspeedsaxial-flow compressors: these well known draw- A;- suitable operating I4 11 and so. cannot rotate, The guide-vanes are thus torsionallydeformed so that the outlet angle relative to the axial direction isadjusted to the full extent of the rotation of the trunnions adjacentthe inner wall of the compressor passage but is adjusted by aprogressively smaller amount along the length of the blade until thereis no adjustment adjacent the outer wall of the passage because theguide-vanes are there anchored to the outer casing.

The ring 411may be rotated by any suitable mechan' under control of adevice sensitive to speed er gtya c ii dition depending on speedso that,at the design ondition, the inlet guide-vanes 14 are not torsionallydeformed at all but as the speed drops from the design condition thetrunnions 34 are rotated to increase thebutlet angle from the inletguide-waves 14- adjacent the inner Wall of the compressor-duct I6.

I claim:

1. A multi-stage axial flow compressor having an annular inner ductwa1land an annular outer duct wall coaxial with. the inner duct wall,said walls together defining an annular compressor-duct between them,and an inlet row of stator-blades, each of which extends from an innerend at the inner duct wall the whole way across the compressor-duct toan outer end at the outer duct wall, is torsionall'y deformable, wherebysaid. ends are angularly displaceable relative to one another about theneutral axis of torsion of the blade,'has said outer end anchoredagainst rotation to said outer duct Wall and has its inner end engagedin said inner duct wall to be rotatable about an axis substantiallyradial to the common axis of the said duct walls.

2. A multi-stage axial-flow compressor having an inner duct wall and anouter duct wall defining an annular compressor duct between them, and aninlet row of stator blades, each of which extends the whole way acrossthe compressor duct, is torsionally deformable, has one of its endsrigidly fastened to said outer duct wall and has its other end pivotallymounted in said inner duct wall.

3. A multi-stage axial-flow compressor having an inner duct wall and anouter duct wall defining an annular compressor duct between them, an.inlet row of stator blades, each of which extends the whole way acrossthe compressor duct, is torsionally deformable, has one of its endsrigidly fastened to said outer duct wall and has its other end pivotallymounted in said inner duct wall, and means to rotate. said other end inits pivotal mounting.

4. A multi-stage axial-flow compressor having an inner duct wall and anouter duct wall defining an annular compressor duct between them, aninlet row of stator blades, each of which extends the whole way acrossthe compressor duct, is torsionally deformable, has one of its endsrigidly fastened to said outer duct wall and has its other end pivotallymounted in said inner duct wall, a crank connected to said other end, aring to engage with the cranks of each of the blades, and means torotate said ring including a device sensitive to the speed of thecompressor, whereby on rotation of said ring the blades are torsionallydeformed.

References Cited in the file of this patent UNITED STATES PATENTS2,460,778 Willgoos Feb. 1, 1949 FOREIGN PATENTS 486,761 Canada Sept. 23,1952

